Cementitious compositions have been used in the construction industry for years. Examples of cementitious compositions include cement, concrete, mortar, grout, and stucco. Stucco is commonly used in the construction of buildings, particularly on the exterior of a building as a siding treatment. A framework such as paper or metal wire conventionally is affixed to a building, for example, and stucco is applied to the framework. Stucco is typically comprised of cement and inert materials such as sand and lime.
A common problem with a cementitious composition such as stucco is that it has a high pH in its wet-mix phase or when newly applied. A high pH (e.g., greater than 9) intrinsically protects against microorganisms and will naturally protect the material from fungi and other microbial colonization. The cementitious composition is gradually neutralized over time, however, and the untreated cementitious composition loses this innate efficacy against microorganisms such as bacteria, algae, mold and fungus. Furthermore, stucco is porous and absorbs moisture, which is particularly attractive to microorganisms.
Grout commonly finds applications in shower and tub enclosures. Moisture conditions facilitate growth of mold and other undesirable microbial growth, marring the appearance of the shower/tub area and causing malodor.
Previous attempts have been made to add antimicrobial agents to cementitious compositions. However, there are problems that have yet to be solved with known antimicrobial cementitious compositions.
The high pH of cementitious compositions places unique demands on the particular choice of an antimicrobial agent. Since the pH of a cured cementitious composition tends to remain very high even after it sets, the particular antimicrobial agent chosen must be very resistant to chemical degradation due to the high pH. Some antimicrobial agents such as triclosan are also particularly sensitive to the combination of high pH and ultraviolet light, such that the antimicrobial agent causes yellowing when the two conditions are present.
Other attempts have focused on the addition of antimicrobial agents to various components added to cementitious compositions, such as fibers (added for strength) or lightweight particles (added to reduce overall density of the cured cementitious article). For example, U.S. Pat. No. 6,162,845 discloses the use of triclosan in fibers for blending with concrete and like materials.
However, this approach adds complexity, as the antimicrobial agent must be engineered to remain durably affixed to the added component while still being available to provide antimicrobial efficacy. Doped additional components then also becomes a required component, adding material and expense.
Another problem with many known antimicrobial agents is that they disrupt the cure chemistry of a cementitious composition. For example, certain antimicrobial agents may be susceptible to coupling with impurities and will lead to possible color changes.
Still another problem with many known antimicrobial agents is that they have poor solubility in a cementitious composition. The agents may leach out of the cementitious composition over time and/or upon exposure to conditions typical of the use environment. Also as a result of poor solubility, some antimicrobial agents cannot be homogeneously distributed within the finished cementitious substrate.